Anesthesia and analgesia will be routinely performed, and standardized for all the study patients. Low doses of the opiate fentanyl (2-3 μg/kg) and the short-acting sedative propofol (20 mg bolus, and 3-6mg/kg/h drip) will be administered at the beginning of the procedure. Rocuronium bromide, a brief acting muscle paralyzer, 0.6mg/kg, will also be used in most patients.